The ubiquitous and ever-increasing occurrence of bacterial extrachromosomal elements or plasmids which confer antibiotic resistance, enhance pathogeniciy or invasiveness, expand physiological capabilities or host range, specify bacteriocin production and/or confer conjugal donor ability is curtailing the effective prevention, diagnosis, and treatment of bacterial disease. Recently, a plasmid has been implicated in the production of exocellular insoluble dextran-like polysaccharides in the cariogenic organism, Streptococcus mutans. Such insoluble polysaccharides are thought to play a critical role in S. mutans-mediated caries formation by providing a matrix which facilitates colonization of the tooth surface by this organism. The research proposed herein is aimed at gathering basic information relative to the plasmid linkage of insoluble dextran-like polysaccharide synthesis in the four sub-species of S. mutans. First, the genetic stability of plsmids conferring this trait will be comparatively examined. Second, a variety of agents which promote the loss of plasmids will be examined for their ability to eliminate selectively insoluble dextran-like polysaccharide production in S. mutans. Third, representative strains of S. mutans and their insoluble polysaccharide-deficient derivatives will be examined for the presence of covalently closed circular DNA. Such plasmid DNA will be characterized with respect to molecular weight, buoyant density, base composition and number of molecules per chromosomal equivalent. Furthermore, attempts will be made to correlate the presence of plasmid DNA with bacteriophage or bacteriocin production. The proposed research is expected to contribute fundamental information concerning plasmid occurrence, structure and function in organisms indigenous to the oral cavity. This work will have implications within the context of the control of bacterial-mediated caries formation, periodontal disease, and microbial colonizaton of the mouth.